Feasibility assessment of removal of heavy metals and soluble microbial products from aqueous solutions using eggshell wastes

The effective removal of heavy metals and soluble microbial products from wastewater is crucial for ensuring a safe environment and good quality human health. The present work investigated the potential of eggshell (ES) waste as an adsorbent for removing heavy metals and soluble microbial products. ES was firstly used to capture heavy metal ions, and the eggshell–metal (ES-M) complex was then applied to remove soluble microbial products (e.g., proteins) from aqueous solution. In this study, bovine serum albumin (BSA) was selected as a model protein-based contaminant. The equilibrium and kinetic characteristics of soluble protein removed by ES were evaluated in batch mode involving parameters such as metal ions (Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺), operating temperatures (277–323 K), and particle size of ES (100–700 µm). The isotherm curves were well-fitted by Langmuir–Freundlich model. As the temperature increased from 277 to 323 K, the maximum binding capacity for BSA increased from 25.22 to 34.28 (mg BSA/g ES-Zn). The negative values of ΔG° indicated the spontaneous nature of the protein adsorption, while the kinetic of protein adsorption followed the pseudo-second-order model. ES functionalized with heavy metal ions acted as an effective pseudo-chelating adsorbent for the removal of soluble protein from wastewater. Chelates of Zn–BSA found on the ES complexes were found to be highly stable, indicating a minimal possibility of secondary pollution caused by these Zn- and BSA-containing ES complexes. The ES-Zn complex can be potentially used as an adsorbent for removing soluble microbial products in wastewater prior to the membrane filtration.